In an electric switch which utilizes make and break contacts, for example, where there is a contact between moveable contacts and stationary contacts, repulsive electro dynamic forces are present due to currents flowing through these contacts. The detailed theory of the causes of generating these forces is well-known in the electric switch art.
When a "fault" current passes through the contact tips, electromagnetic repulsive forces of very high magnitude are generated at the contact tips. These forces cause the contact tips to lift from their normally closed position. The opening of the contacts ignites the electric arc with core temperatures exceeding the melting points of the moveable and stationary contacts. The contacts are thus welded and render the electric switch damaged, and in worse situations, inoperable or malfunctional. Further, when the electric transfer switch is closed, the moveable and stationary contacts will bounce and strike with each other. The bouncing and striking also cause the electric arcs and consequently cause welded contacts.
In addition, the very same "fault" current also causes the moveable contacts to attract to each other so that the moveable contacts come closer to each other. The neighboring moveable contacts will also bounce and strike with each other which cause electrical arc, and eventually the neighboring moveable contacts are welded together which render the electrical transfer switch inoperable.
Accordingly, one of the objects of an electric transfer switch is to maintain the contact between the various contacts, such as between the moveable contacts and the stationary contacts, in a normal current situation so as to eliminate the electric arc or other negative effects in damaging the contacts.
Another object is to maintain contact between the moveable contacts and the stationary contacts under a "fault" current so as to prevent the contact tips of the moveable contacts and the stationary contacts from bouncing and striking with each other.
Conventional electric switches have not been able to address the above concerns or solve these problems. U.S. Pat. No. 4,849,590 discloses a way of keeping the contacts shut. However, the disclosed invention relied on providing a small blow-off force to blow an arc into an arc chamber when the contacts separate.
U.S. Pat. No. 5,073,764 discloses a twin-contact type current limiting apparatus. However, it actually increases the contact open force by routing the current.
The present invention provides a catch for an electric transfer switch or other types of devices, such as circuit breakers, which solves these and many other problems associated with existing electric transfer switches or circuit breakers.